There is tremendous interest unmanned underwater vehicles (UUVs) for remotely performing functions such as exploring, sensing and mapping, or retrieving items e.g. UUVs allow a mother ship to safely gain access to denied areas such as extremely shallow water, very poor acoustic conditions, or mined waters. Therefore, UUVs provide unique capabilities and extend the reach of a mother ship whilst reducing the risk to the mother ship and its crew.
Existing UUVs encounter many challenges during operations which include precise station keeping, tight tactical maneuvers in hostile environments such as mined waters as well as retrieval of UUVs for mother ships. Existing UUVs generally employ a single propeller with the control surfaces at the stern to provide standard maneuvering capability but not the ability to face the operations challenges. This results from traditional control surfaces requiring forward speed in order to produce turning moments. In addition, the residual torque generated by the propeller needs to be balanced by the control surfaces, which generates additional drag for the vehicle and thus increases the power consumption.
The prior art of Haselton, as shown in FIGS. 1A and 1B, includes a propeller arrangement that provides a solution to many of the abovementioned challenges. FIGS. 1A and 1B show the Haselton submersible vehicle 10 having a vehicle body 11 with bow and stern hub propellers 21 and 22. According to this prior art design, the propellers 21 and 22 rotate in a contra-rotating mode using cyclic blade pitch to produce side forces. This design provides both conventional maneuvers such as forward/reverse, forward/reverse turns, as well as unconventional maneuvers such as sideways translation, turning-in place and station-keeping/hovering in place.
However, the Haselton vehicle payload has been sacrificed because of the helicopter swash plate assembly used to implement the cyclic-pitch system. The swash plate assembly which includes linkages to for tilting the propellers occupies more space than desired. The complexity of this design may cause reliability concerns. This design also utilizes a lot of energy, which is not desired. For example, in order to achieve stability, both propellers 21 and 22 should be operated contemporaneously. When only one propeller is operated, a residual torque is generated which must be balanced by a control surface such as a stabilizer 30. This results in increasing the power consumption of the vehicle 10. Also, the forward propeller 21 operates in an inefficient environment because its positioning facilitates a minimal boundary layer flow. In addition to those inefficiencies, the propellers 21 and 22 are separated so that the aft propeller 22 can't recover the swirl energy from the forward propeller 21, leading to even more energy losses. Thus, it is desired to have a submersible vehicle that provides maneuverability similar to the Haselton vehicle, but has a simpler design that does not sacrifice the payload, and is more energy efficient.